1. Field of the Invention
This invention relates to the construction of integrated circuit structures. More particularly, this invention relates to an improved method for forming metallization strips on an integrated circuit structure.
2. Description of the Prior Art
In the construction of integrated circuit structures, metallization strips or lines are usually provided over an insulation layer to interconnect, through vias or contacts formed in the insulation layer, various circuit elements located below the insulation layer. Conventionally, such metals strips have been formed by first depositing a metal layer and then providing a pattern of photoresist over the metal layer. The metal layer was then selectively wet etched to remove exposed metal leaving metal strips beneath the photoresist.
However, as the size of the integrated circuit structures became smaller with very large scale integration (VLSI), the metallization strips, as well as the spacing between strips, became narrower. This, in turn, made it more difficult to use wet etching techniques to produce such narrow metal strips due to the difficulty in accurately controlling the extent of the wet etch because of the isotropic nature of wet etching. The prior art, therefore, adopted more costly but also more active dry etching techniques, such as reactive ion etching.
Other processes have also been used in the prior art, such as a so-called lift off process in which a removable mask, such as an organic material, is applied over an insulating surface to leave mask portions in the areas between the desired metal strips. A metallization layer is then applied over the patterned mask and the insulating layer. Finally, the removable mask is removed or "lifted" off the insulating layer together with those portions of the metallization layer located over the removable masks leaving the desired metal strips.
Yet other techniques have been proposed, such as the use of multiple metal layers and sputter etching as described in Reissue Patent No. 29,947.
However, from a standpoint of process economics, it would be preferable to use wet etching processing if the desired accuracy of the dimensions of the metal strips can be maintained.